Isoprenoid is a substance that plays a critical role in living organisms, which is used to maintain cell's fluidity, electron transfer and another metabolism. Isoprenoid includes a diverse group consisting of more than 40,000 products, many natural isoprenoids and synthetic isoprenoids of which are used as medicines, cosmetics, perfumes, pigments, coloring agents, fungicides, preservatives, functional foods and fine chemical intermediates.
Further, in a natural state, isoprenoid is synthesized by continuous condensation reaction of isopentenyl diphosphate (IPP), which is a precursor thereof, and dimethylallyl pyrophosphate (DMAPP), which is an isomer thereof. Two routes are known for the precursor. Except for plants, eukaryotes generally use a mevalonate-dependent pathway (MVA) to convert acetyl coenzyme A (acetyl-CoA) to IPP. Here, the IPP later becomes an isomer as DMAPP. Although there are some exceptions, prokaryotes typically use the only mevalonate-independent pathway or the deoxyxylulose-5-phosphate pathway (MEP) to generate IPP and DMAPP. Plants use both of MVA and MEP pathways.
Typically, isoprenoid has been prepared via extraction from natural sources such as plants, microorganisms, and animals. However, yields are usually very low because there are many severe limitations to extraction. First, most isoprenoid accumulates only in small amounts under natural conditions. Second, feed organisms are typically not suitable for mass-scale cultivation processes which are necessary to produce commercially useful amounts of desired isoprenoids. Third, isoprenoid extraction requires any toxic solvent, and particular attention should be paid to the handling and processing of this solvent, so there are many difficulties in the commercial production of isoprenoid.
Moreover, a sesquiterpene, a class of isoprenoid extracted from plants, is known to have important medical and industrial properties (Berger, 2009; Dhingra et al., 2009; Muntendam et al., 2009). Farnesene has recently been developed as biofuel precursors due to hydrogenation reactions of farnesene (Renneger and McPhee, 2008). But, only naturally small amounts thereof are produced. Accordingly, it is expected that metabolic engineering is an alternative pathway for mass production of such rare and valuable compounds from E. coli and yeast. It is necessary for developing technology to mass-produce farnesene with a significant industrial value.